1. Field of the Invention
The present invention generally pertains to converter circuits, and in particular to automatic rectification in converter circuits.
2. Discussion of the Related Art
A circuit arrangement for automatic rectification of voltages present at the secondary side of a transformer in a d.c. voltage/d.c. voltage converter is shown in FIG. 7 on pages 496-498 of the 1991 edition of the conference book INTELEC 91, CH 2970-2/910000-0495. In this circuit arrangement, rectification of voltages at the secondary side occurs using two circuit elements that are cross-driven. Thus, control voltages for the respective control input of the circuit elements are taken at the terminals of the coils of the transformer arranged at the secondary side.
This known circuit arrangement has the disadvantage that the control voltage for the circuit elements is not kept constant and is present during the entire switching cycle. This circuit arrangement is also inappropriate for low voltage converters. Given a voltage such as 2.5 or 1.8 volt, a sufficient driving is no longer present for the rectifiers on the secondary side of the converter.
The published patent application German 43 15 906 discloses a current supply circuit having an inductive circuit element for storing electrical energy with a circuit device for periodically supplying the energy to the circuit element. Given this circuit arrangement, occurring transverse currents are prevented by a logical blocking circuit. The free-wheel rectification component is controlled on the basis of this blocking circuit, which is comprising a plurality of gate elements and driver elements. The blocking circuit is driven via a plurality of circuit units.
A control voltage that is too low results in an insufficient modulation of the circuit elements. The efficiency of the circuit worsens as a result of the insufficient modulation.
Accordingly, it is an object of the present invention to offer a circuit and method for automatic rectification in converters for low output voltages.
It is another object of the present invention to offer a circuit and method for automatic rectification in converters, wherein the circuit elements are securely modulated for low output voltages.
It is a further object of the present invention to offer a circuit and method for automatic rectification in converters that requires very little capital outlay.
These and other objects of the invention will become apparent from a careful review of the following detailed description of the preferred embodiment, which is to be read in conjunction with a review of the accompanying drawing figures.